Hydrostatic work support means for grinders

ABSTRACT

Work support means for grinder having a rotatable grinding wheel comprising a pair of hydrostatic workheads having confronting workpiece engaging members adapted for relative axial movement to support a workpiece. At least one of the workheads includes a support member having a part-spherical seat, a clamping member having a part-spherical face contoured to conform to said seat which is enlarged to define a small part-spherical chamber for fluid under pressure. Means is provided for mounting the clamping member for a limited universal movement relative to the support member thereby allowing accurate alignment of the workpiece relative to the axis of rotation of the grinding wheel.

United States Patent [72] Inventor Otto Weissing Towson, Md. [21 1 Appl. No. 729,204 (22] Filed May 15, 1968 [45] Patented Apr. 13, 1971 [73] Assignee SKF Industries, Inc,

King of Prussia, Pa.

[54] HYDROSTATIC WORK SUPPORT MEANS FOR GRINDERS 8 Claims, 9 Drawing Figs.

[52] U.S.Cl 51/237, 51/105 [51 int. Cl B25b 5/00, B24b 5/00 [50] Field of Search 51/289, 236, 237; 279/16 [56] References Cited UNITED STATES PATENTS 467,294 1/1892 Mills 279/16 Primary Examiner-Harold D. Whitehead Attorney-Howson and Howson ABSTRACT: Work support means for grinder having a rotatable grinding wheel comprising a pair of hydrostatic workheads having confronting workpiece engaging members adapted for relative axial movement to support a workpiece. At least one of the workheads includes a support member having a part-spherical seat, a clamping member having a part-spherical face contoured to conform to said seat which is enlarged to define a small part-spherical chamber for fluid under pressure. Means is provided for mounting the clamping member for a limited universal movement relative to the support member thereby allowing accurate alignment of the workpiece relative to the axis of rotation of the grinding wheel.

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Patented A ril 13, 1971 3,514,914

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HYDROSTATIC WORK SUPPORT MEANS FOR GRINDERS This invention relates generally to grinding apparatus and more particularly to a new and improved hydrostatic work support means for grinders.

The present invention is particularly directed or applicable to grinders used for grinding workpieces having a surface of revolution such as rings or rollers for rolling bearing assemblies. These grinding apparatus conventionally comprise a base or bed, work support means for rotatably supporting the workpiece, such as a roller, and a grinding wheel assembly mounted on the bed for movement relative to the workpiece in one direction to grind the workpiece during the grinding cycle and in a retract direction to withdraw the grinding wheel assembly after completion of the grinding cycle. In these conventional grinding apparatus the work support means generally includes a first workhead supported on a spindle which is connected to drive means for rotating the workhead and a second workhead adapted to axial movement relative to the first workhead so that the workpiece may be selectively positioned between the workheads. The spindle of one workhead is conventionally supported in roller bearing assemblies and the tailstock is also mounted in a bearing assembly for movement in an axial direction. In these conventional grinders, the workpiece is supported in some instances between conical centers and in other cases the workpiece is supported between shoes mounted on the spindle and tailstock. In the former method, each of the workheads is usually provided with a pointed conical center element which engages in centering taps or holes in opposite axial end faces of the workpiece to align the axis of rotation of the workpiece with an axis through the center of the workheads. This arrangement provides a preset live center" of rotation of the workpiece during the grinding cycle. In some grinding apparatus of the above type the workpiece is supported between a shoe carried by the driving spindle of the tailstock and a shoe mounted on the axially movable workhead.

The principal disadvantage noted in prior grinding apparatus of the above types in the grinding of workpieces having a spherical surface of revolution such as roller or rings for rolling bearing assemblies is the fact that it is difficult to precision grind these workpieces and maintain the out-ofroundness and end face to surface of revolution runout (outof-squareness) within very narrow limits, for example in the range of less than one micron. This problem is attributable to several factors. For example, the roundness of the finish ground workpiece was limited by the geometric accuracy, the looseness and the surface finish of bearing elements usually ball or roller bearings supporting the workheads, which factors in bearing assemblies vary over a period of extended use. Furthermore, in grinding apparatus of the above-type the center holes in the workpieces had to be formed very accurately and if they were not located precisely on the axis of rotation of the workpiece, the out-of-roundness of the finish ground workpiece will not fall within tolerable limits. Moreover, if the centers of the workheads, which, it has been found are difficult to maintain in precise alignment, are slightly misaligned, the squareness (side runout) of the finished workpiece will also be adversely affected.

A disadvantage in grinding apparatus employing shoe supports is that for rolling bodies with convex spherical end faces, zero runout between the end faces and the surface of revolution can be obtained only at one ideal diameter for which the shoe supports have been set. As a practical matter, it is impossible to grind to this ideal diameter every time and consequently a runout condition is produced on every roller ground to a diameter other than the ideal diameter in most instances.

The present invention provides work support means for grinding apparatus of the above-type which eliminates the problems noted above and makes it possible to grind workpieces with an out-of-roundness of less than one micron. To this end, the work support means of the present invention comprises a first workhead adaptedto engage one axial end face of the workpiece, for example, a roller, the first workhead being carried by a spindle mounted for rotation in hydrostatic bearings. The work support means further includes a second workhead having a work engaging surface or face adapted to engage and confront an axial end of the workpiece and a spherical portion adapted to seat in a spherical seat to provide a liquid or gas pressurized, hydrostatically lubricated spherical thrust bearing for self-alignment action. The second workhead is adapted for movement in an axial direction relative to the first workhead to facilitate positioning of the workpiece between the workheads, the workheads in the operative position engaging opposite axial end faces of a workpiece such as a roller. For optimum self-alignment action, the center of the spherical portion of the second workhead is located on the workpiece engaging surface so that this center is coincident with the axis of the workpiece and drive spindle of the first workhead whereby all of the centers of rotation are on the same axis and there is no wobbling of the workpiece during the grinding cycle. Since the work engaging portions of the workheads engage the axial end faces of the workpiece directly, the task of forming centers in the workpiece is eliminated and the corresponding potential inaccuracies due to misalignment of the tap centers is eliminated. Moreover, it has been found that the out-of-roundness may be controlled within precise limits even though the ends of the workpiece may be several thousandths of an inch out of parallel and it is noted that the workpiece need not be supported with its axis aligned with the axis of the work holding clamping member. This is due to the fact that the spherical clamping member has a limited degree of universal movement.

Additionally, hydrostatic lubrication of all bearing surfaces supporting the workheads and the self-alignment feature of the spherical workhead provide for greater stiffness, more accurate rotation and lower friction in the support for the workpiece.

With the foregoing in mind, an object of the present invention is to provide a work support means for grinding apparatus used to grind workpieces having a surface of revolution such as rings or rollers for bearing assemblies, with support means is characterized by novel features of construction and arrangement to accurately and precisely support the workpiece to facilitate grinding with an out-ofroundness of less than one micron.

Another object of the present invention is to provide a support means for a grinder which is of comparatively simplified construction and wherein the vurkpieces may be fed and removed from the grinding apparatus easily and quickly.

These and other objects of the present invention and the various features and details of a grinder incorporating work support means in accordance with the present invention are more fully set forth with reference to the accompanying drawings, wherein:

FIG. I is an end view of a grinding apparatus in accordance with the present invention;

FIG. 2 is a side view of the grinding apparatus shown in FIG. 1;

FIG. 3 is an enlarged sectional view of the work support arrangement of the present invention taken on line 3-3 of FIG. 1;

FIG. 4 is a sectional view taken on line 4-4 of FIG. 2;

FIG. 5 is a view of the rotating workhead as viewed along line 55 of FIG. 3;

FIG. 6 is a sectional view taken on line 6-6 of FIG. 5;

FIG. 7 is an enlarged sectional view taken on line 7-7 of FIG. 6;

FIG. 8 is a side elevational view of one of the hydrostatic work heads with parts broken away to show some of the internal construction thereof; and

FIG. 9 is a schematic showing of the circuitry of the workheads.

Referring now to the drawings and particularly to FIGS. 1 and 2 thereof, there is shown a grinding apparatus generally designated by the numeral incorporating a work support means in accordance with the present invention. The grinding apparatus includes a base or bed 12 and work support means for rotatably supporting therebetween a workpiece W having a surface of revolution such as the rollers or rings of a bearing assembly. A grinding wheel assembly 16 including a rotatably mounted grinding wheel 18 is mounted on the base 12 and is selectively movable toward the workpiece during the grinding cycle and away from the workpiece W after completion of grinding. The grinding apparatus 10 further includes a supply bin or chute 20 for annular workpiece W and a pivotally mounted feed assembly 22 for automatically displacing workpieces W from the supply chute 20 and positioning them between the workheads of the work support means.

The work support means comprises a pair of hydrostatic workheads 30 and 32 between which the workpiece W is supported. The first hydrostatic workhead 30 as best illustrated in FIGS. 3 and 7 comprises a nose element 34 mounted on one axial end of a spindle 36 and a drive plane 38 carried by the nose section adapted to engage one axial end face of the workpiece W. The spindle 36 which is rotatably supported in an elongated hollow housing 40 mounted on the base, is rotated in the housing by suitable drive means including, the present instance, a belt transmission 42 operatively connected to one end of the spindle 36. The spindle 36 has enlarged sections 360 and 36b adjacent opposite axial ends which define bearing support surface journaled in annular bearing pads 44 and 46 in the housing40. In the present instance, the spindle bearing surfaces are hydrostatically lubricated to provide for accurate rotation of the spindle, lower friction and higher radial stiffness. To this end, the bearing pad 44 is provided with a plurality of circumferentially spaced pockets 45 and the bearing pad 46 is similarly provided with a plurality of circumferentially spaced pockets 47, the pockets 45 and 47 confronting the enlarged spindle sections 36a and 36b. Suitable channel means is provided in the housing to convey lubricant under pressure to the pockets 45 and 47 for hydrostatically lubricating the spindle bearing surfaces. Further, as illustrated in FIG. 8, the spindle 36 has an enlarged annular flange 49 at its inner end and means in the form of an annular passageway for lubricant under pressure is provided adjacent the radial end faces of the flange 49. In the present instance as illustrated in FIG. 8, a circumferentially extending recess 51 is provided in the axial end face of the pad 46 facing the flange 49 defining one pressure chamber and the detachable head of the housing 40 has an annular groove 55 therein defining the other pressurized lubricant channel facing the outer radial face of the flange 49. These pressurized channels are adapted to receive lubricant under pressure during operation of the spindle.

The hydrostatic workhead assembly 32 is best shown in FlGS. 3 and 6. The workhead of this assembly is adapted for axial movement relative to the first workhead 30 between a forward, workpiece engaging position (FIG. 3) during the grinding cycle, and a retracted position (not shown) after completion of grinding to permit positioning of workpieces between the workheads for successive grinding cycles. To this end, the workhead 32 is carried on one axial end of a shaft member 50 which in turn is mounted for axial movement in the bore 52 of the housing 54 on the base of the grinder. The housing 54 may be mounted on a cross slide or way 56 on the base for movement of the second workhead assembly relative to the base for rough adjustment or positioning as explained in detail below. Further, as illustrated in FIG. 3, the shaft member 50 is provided with a longitudinally extending groove 60 within which a key 620 engages to guide the shaft member 50 during reciprocating back and forth movement in the housing 54 and prevent rotation thereof when the hydrostatic workhead 32 is in its forward limit position during a grinding cycle. The shaft member 50 is supported on bearings in the housing comprising, in the present instance, a relatively short sleeve 62 mounted in the forward end of the housing and longer sleeve member 64 mounted in the rear end of the housing. The sleeves 62 and 64 are provided with circumferentially extending lubrication channels 66 and 68 respectively which confront the outer surface of the shaft member 50 and receive a lubricant from a pair of lubrication ports 70 and 72 in the housing 54 which communicate with the lubrication channels '66 and 68 respectively. These ports may be filled with a lubricant to provide hydrostatic lubrication of the bearing surfaces of the sleeves 62 and 64.

The shaft member 50 is movable longitudinally in the bore of the housing to position the second hydrostatic workhead 32 between forward and retracted limit positions. To this end, in the present instance, a rod 76 is mounted on the inner face of the outer cap closure member 78 closing the back end of the housing 54, the rod mounting at its inner end a piston 80 which engages in a generally cylindrical chamber 82 formed in the shaft member 50. The rod 76 is provided with a pair of axial passageways and 92, one passageway 90 extending the length of the rod 76 and communicating withthe inner section 82a of the chamber 82 and the other passageway 92 communicating with the outer section 82b of the chamber 82 through a short radial passage 88.

There is illustrated schematically in FIG. 9, the circuit for effecting axial movement of the workhead 32 and also for hydrostatically lubricating the various bearing surfaces, As illustrated, the circuit includes a motor M for driving a pump P to deliver fluid from reservoir R through line 130 to line 132 which communicates through branch line 134 with the workhead 30 and through branch line 136 with the workhead 32. Line 134 feeds three conduits 138, 140, and 142, which are connected to the housing and through suitable passageways in the housing. feed fluid to the pockets 45 and 47 and the lubricant pressure chambers 51 and 55. Line 136 also has two branches 136a and 136!) connected to the passageways 90 and 92 of the rod 76. A solenoid operated four-way valve is provided in the branches 136a and 13617 for selectively controlling flow through the passageways 90and 92 whereby the direction of axial movement of the workhead 32 may be controlled. By this arrangement, when it is desired to move the shaft member 50 in a direction to position the hydrostatic workhead 32 in its forward position, the solenoid A is energized whereby fluid flows through the passageway 90 to the inner section 82a of the chamber 82, the passageway 92 communicating with the reservoir to vent fluid from the outer section 82!) whereby the shaft 50 is displaced axially of the housing 54 and to the left with respect to FIG. 3, to engage an axial end face of the workpiece W positioned between workheads 30 and 32. The hydraulic pressure is selectively chosen to provide a clamping force great enough so that the friction force between the faces of the workpiece W and the workheads exceeds the grinding force applied by the grinding wheel. Now when it is desired to retract the shaft member 50 after completion of the grinding, solenoid B is energized whereby high pressure fluid flows into the outer section 82b of the chamber 82 through the passageway 92 and the fluid in the inner section 82a of the chamber 82 is vented to the reservoir through the passageway 90.

Considering now the structural details and arrangement of the hydrostatic workhead 32 and referring particularly to P16. 6 of the drawing, which shows these details, the workhead 32 includes a support member secured to the outer axial end face of the shaft 50 by suitable screw-type fasteners and having a reduced pilot portion 102 at one axial end which seats in a socket 104 in the axial end face of the shaft 50 and a spherical seat 106 in its opposite axial end face. A rotatable clamping member 108 having a spherical face 110 contoured to conform to the seat 106 is supported on the seat by means of an inner annular retaining ring 112 and an outer annular collar 111. The inner retaining ring has a radially inwardly directed inner circumferential flange 114 confronting a shoulder 116 in the outer face of the clamping member and a radially outwardly directed outer circumferential lip 118 which engages in an annular pocket 120 in the outer collar 111. In the present instance, the pocket 120 is defined by an undercut 121 in the outer face of the collar 111 and a radial face 123 of the support member 100. A predetermined small clearance is provided between the lip 118 and the walls defining the pocket 120 in the outer retaining collar to permit a small amount of universal movement of the clamping member 108. The clearance may be in the order of 0.006 inch between the inner wall 1180 of the lip 118 and the confronting wall 121a of the undercut 121 and 0.002 inch between the outer wall 118b of the lip 118 and the radial face 123 of the support member 100. A workpiece engaging member in the form of a button 130 having an arcuate convex workpiece engaging face is mounted centrally of the clamping member 108 in a holder 130a. As best illustrated in H0. 7, the end face of the workpiece is concave and the center of the hemispherical face 110 of the clamping member is located in the face of the workpiece engaging button 130. This arrangement provides for maximum self-alignment action.

The spherical seat 106 in the support member 100 is enlarged to define a small spherical chamber 132 which communicates through a conduit 134 in the support member 100 for receiving high pressure fluid from a suitable source to support the clamping member for rotation during the grinding cycle. To this end as best illustrated in FIG. 9, the channel 134 is connected by a line 144 to the source of high pressure fluid. A drain line 145 communicates at one end with the reservoir R and at its opposite end with a drain channel 147 in the support member 100, the channel 147 being in fluid communication with an annular passageway 149 adjacent the inner edge of the retaining ring 112 to drain off lubricant from the spherical chamber 132.

While a particular embodiment of the present invention has been illustrated and described herein, it is not intended to limit the invention and changes and modifications may be made within the scope of the following claims.

lclaim:

1. Work support means for a grinder comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in said support member and means for supporting said clamping member in said support member comprising an inner annular retaining ring and an outer annular collar, the inner retaining ring having a radially inwardly directed circumferential flange confronting a shoulder in the outer face of the clamping member and a radially outwardly directed outer circumferential lip which engages in an annular pocket in the collar, the pocket being defined by an undercut in the outer face of the collar and a I radial face of the support member, means defining a predetermined small clearance between said walls defining the pocket permitting a small amount of universal movement of the clamping member.

2. Work support means for a grinder comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in said support member, said workpiece engaging member for said one workhead being in the form of a button mounted centrally of the clamping member opposite said spherical face thereof, said button having an arcuate convex work engaging face adapted to engage in a concave axial end of the workpiece.

3. Work support means as claimed in claim 2 wherein the center of the hemispherical face of the clamping member is located in the arcuate workpiece engaging face of said button.

4. Work support means for a grinder comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in said support member, said means for effecting axial movement of said one workhead including a housing, a shaft member mounted in said housing, said shaft member having a chamber therein, a rod mounted in said housing having a piston portion engaging in said chamber dividing said chamber into inner and outer sections, a pair of passages in said rod, one of said passages communicating at its inner end with one section of the chamber and the other passage communicating at its inner end with the other section of said chamber, and means for selectively delivering fluid under pressure to said chamber sections thereby to effect axial movement of said shaft member in said housing in either axial direction.

5. Work support means for a grinder comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mJunted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in sa d support member and a pair of annular bearing pads mounted in said housing for said other workhead, wherein said spindle has enlarged sections adjacent opposite axial ends thereof defining bearing support surfaces confronting said pads, means defining a plurality of circumferentially spaced pockets in said bearing pads connected to a suitable supply of fluid for pressurizing said pockets.

6. Work support means as claimed in claim 5 wherein said spindle has an enlarged annular flange at one end thereof adjacent the workpiece engaging member for said other workhead and one of said bearing pads is mounted adjacent said flange and has an annular passageway in one radial end face thereof confronting said flange and including means connecting said annular passageway to a source of fluid thereby to pressurize the same.

7. Work support means for a grinder having a rotatable grinding wheel comprising a pari of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, said workheads being the sole support of the workpiece during the grinding cycle, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber, the seat of said clamping member in a circular zone around said chamber being in pressure applying relation with the face of said clamping member during the grinding cycle, means for supplying a fluid under pressure to said chamber to hydrostatically support the clamping member for rotating movement in said support member and means mounting said clamping member in said support member in a manner permitting limited universal movement of said clamping member thereby allowing accurate alignment of said workpiece relative to the axis of rotation of the grinding wheel.

8. Work support means for a grinder having a rotatable grinding wheel comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, said workheads being the sole support of the workpiece during the grinding cycle, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in said support member, the seat of said clamping member in a circular zone around said chamber being in pressure-applying relation with the face of said clamping member during the grinding cycle and means mounting said clamping member in said support member in a manner permitting limited universal movement of said clamping member thereby allowing accurate alignment of said workpiece relative to the axis of rotation of the grinding wheel. 

1. Work support means for a grinder comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, at least one of said workheads including a support member having a partspherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in said support member and means for supporting said clamping member in said support member comprising an inner annular retaining ring and an outer annular collar, the inner retaining ring having a radially inwardly directed circumferential flange confronting a shoulder in the outer face of the clamping member and a radially outwardly directed outer circumferential lip which engages in an annular pocket in the collar, the pocket being defined by an undercut in the outer face of the collar and a radial face of the support member, means defining a predetermined small clearance between said walls defining the pocket permitting a small amount of universal movement of the clamping member.
 2. Work support means for a grinder comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in said support member, said workpiece engaging member for said one workhead being in the form of a button mounted centrally of the clamping member opposite said spherical face thereof, said button having an arcuate convex work engaging face adapted to engage in a concave axial end of the workpiece.
 3. Work support means as claimed in claim 2 wherein the center of the hemispherical face of the clamping member is located in the arcuate workpiece engaging face of said button.
 4. Work support means for a grinder comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in said support member, said means for effecting axial movement of said one workhead including a housing, a shaft member mounted in said housing, said shaft member having a chamber therein, a rod mounted in said housing having a piston portion engaging in said chamber dividing said chamber into inner and outer sections, a pair of passages in said rod, one of said passages communicating at Its inner end with one section of the chamber and the other passage communicating at its inner end with the other section of said chamber, and means for selectively delivering fluid under pressure to said chamber sections thereby to effect axial movement of said shaft member in said housing in either axial direction.
 5. Work support means for a grinder comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in said support member and a pair of annular bearing pads mounted in said housing for said other workhead, wherein said spindle has enlarged sections adjacent opposite axial ends thereof defining bearing support surfaces confronting said pads, means defining a plurality of circumferentially spaced pockets in said bearing pads connected to a suitable supply of fluid for pressurizing said pockets.
 6. Work support means as claimed in claim 5 wherein said spindle has an enlarged annular flange at one end thereof adjacent the workpiece engaging member for said other workhead and one of said bearing pads is mounted adjacent said flange and has an annular passageway in one radial end face thereof confronting said flange and including means connecting said annular passageway to a source of fluid thereby to pressurize the same.
 7. Work support means for a grinder having a rotatable grinding wheel comprising a pari of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, said workheads being the sole support of the workpiece during the grinding cycle, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seat, said seat being enlarged to define a small part-spherical chamber, the seat of said clamping member in a circular zone around said chamber being in pressure applying relation with the face of said clamping member during the grinding cycle, means for supplying a fluid under pressure to said chamber to hydrostatically support the clamping member for rotating movement in said support member and means mounting said clamping member in said support member in a manner permitting limited universal movement of said clamping member thereby allowing accurate alignment of said workpiece relative to the axis of rotation of the grinding wheel.
 8. Work support means for a grinder having a rotatable grinding wheel comprising a pair of hydrostatic workheads having confronting workpiece engaging members between which a workpiece is supported at opposite axial ends, means mounting said workheads for relative axial movement to permit positioning and gripping of the workpiece during a grinding cycle and removal thereof after grinding, said workheads being the sole support of the workpiece during the grinding cycle, at least one of said workheads including a support member having a part-spherical seat in one axial end face thereof, a clamping member having a part-spherical face contoured to conform to said seat and mounted for rotational movement in said seAt, said seat being enlarged to define a small part-spherical chamber adapted to be supplied with a fluid under pressure to hydrostatically support the clamping member for rotating movement in said support member, the seat of said clamping member in a circular zone around said chamber being in pressure-applying relation with the face of said clamping member during the grinding cycle and means mounting said clamping member in said support member in a manner permitting limited universal movement of said clamping member thereby allowing accurate alignment of said workpiece relative to the axis of rotation of the grinding wheel. 